Screws have different features based on the objects to be drilled. These features are aimed at to have preferred drilling speed, high dregs removing rate, and easiness in drilling operation. However, the dregs generated in drilling will be left in the drilling hole, but this residue left in the hole is possible to cause that the object to be drilled cracks. The main reason of such a defect is that the dregs left in the hole will further expand the hole to have a larger size, as a result the object to be drilled cracks. A further reason is that the outer diameter of the screw head is larger than an inner diameter of the hole. Then the screw head is embedded into the hole, it is possible that the hole will crack. It is desired to cut, expand and smooth the hole before embedding the screw head so that the larger screw head can be flatly embedded into the hole with an easy and comfortable operation. Furthermore, no cracking forms and the edge of the hole is smooth.